app 状态解释 & push执行情况

• 
  
• UIApplicationStateActive 
• The app is running in the foreground and currently receiving events. 
• 在前台

• UIApplicationStateInactive 
• The app is running in the foreground but is not receiving events. This might happen as a result of an interruption or because the app is transitioning to or from the background. 
• 前后台过渡阶段

• UIApplicationStateBackground
• The app is running in the background. 
• 在后台

push执行情况：

收到push的两种情况

一：收到push的时候程序正好在前台，直接执行receivePush方法。

二：收到push程序不在前台（可能后台，可能杀死状态。。），弹出push通知。

点击push通知的两种情况

一：程序还活着（可能是前台状态，可能是后台状态。。）：点击push通知会执行receivePush方法。

二：程序被杀死了：点击push会执行didFinishLaunchingWithOptions，但是却不会执行receivePush方法，需要在didFinishLaunchingWithOptions方法里边手动去执行。。